Electrical communication in and out of an array of tightly pitched wires can be difficult. It can be difficult because aligning an electrical bond pad to each wire without accidentally connecting to an adjacent wire can require a machine capable of high accuracy.
One structure for electrically connecting to wires of an array is called a multiplexing/demultiplexing architecture (a “mux/demux architecture”). The mux/demux architecture does not need an electrical bond pad to be connected or aligned with each wire of an array. Instead, one bond pad is typically connected to all of the wires of the array.
This one bond pad, however, does not allow communication with each wire of the array individually. To differentiate between wires, an address element, such as a transistor, can be contacted with each of the wires. For a 16-wire array, for instance, four transistors can be contacted with each wire. By selectively turning the transistors on and off, only one of the 16 wires can be permitted to communicate with the one bond pad. Manufacturing this mux/demux architecture is typically less expensive and more reliable than connecting a bond pad to each wire.
In FIG. 1, for instance, an array of wires 102 with a pitch 103 of about 1000 nanometers is electrically connected to one common node 104. A pitch is a distance between wires plus a width of one of those wires. Thus, a pitch of an array having wires that are one millimeter wide and spaced two millimeters apart is three millimeters. Wires 106 of the array 102 can be communicated with separately using a mux/demux architecture shown at numeral 108. This mux/demux 108 has four different address circuits 110, 112, 114, and 116, each of which communicates with a set of transistors 118 through two address lines. These address circuits can turn on or off the transistors 118 to which they are connected. By turning the transistors 118 on and off, only one of the wires 106 will have the same voltage as the voltage supply 120, while the rest of the wires 106 will have no voltage. Thus, only one of the wires 106 can be selected and therefore have the same voltage as the voltage supply 120.
For example, a third wire 122 can be selected if all four of the transistors 118 that are in contact with the third wire 122 are turned on. The transistors 118 of the third wire 122 are turned on by turning the address circuit 110 on, the circuit 112 on, the circuit 114 off, and the circuit 116 on. When on, the transistors 118 on the “Logical YES” side of each of the address circuits turn on and on the “Logical NOT” side turn off, and vice-versa. Address wires 124, 126, 128, and 130 are used to turn the address circuits 110, 112, 114, and 116 on or off, respectively.
One problem with this mux/demux architecture 108 is that it uses address elements (like transistors, diodes, and resistors) that typically need to be aligned with the wires during fabrication. Aligning these elements with the wires can be accomplished with typical processing machines if the wires of the array have a large enough pitch 103. For smaller pitches, however, the address elements of the mux/demux architecture 108 may not be alignable with wires of the array.
There is, therefore, a need for small-pitched devices and methods for addressing them electrically.
The same numbers are used throughout the disclosure and figures to reference like components and features.